1. Field of the Invention
The present invention relates generally to a laser beam processing apparatus that applies desired laser beam processing by irradiating a laser beam to a work to be processed, and, more particularly, to a laser beam processing apparatus employing a multi-branching and fiber-transmission scheme.
2. Description of the Related Art
Conventionally, in the field of laser beam processing such as laser welding and laser marking, to execute multi-point simultaneous processing or multi-position processing, a scheme is employed according to which: a laser beam generated by one laser oscillator is branched into a plurality of laser beams simultaneously or non-simultaneously (in a time-division manner); the branched laser beams are transmitted respectively in optical fibers to remote sites for processing; and the laser beams are applied to desired processing points.
Until the present, a YAG laser is used for a laser oscillator employing the above scheme. The YAG laser uses a rod of a YAG crystal doped with a rare-earth element, so called a YAG rod, as an active medium thereof. An active element contained in a YAG rod is optically pumped by applying an excitation ray to a side face or an end face of the YAG rod. A YAG laser beam is taken out by resonance-amplifying using an optical resonator an oscillated light beam having a predetermined wavelength emitted from the YAG rod in the axial direction. The YAG laser beam oscillation-outputted from the YAG laser is split into a plurality of branched laser beams using a beam splitter for simultaneous branching, or the optical path thereof is switched using a movable mirror among a plurality of branch paths for non-simultaneous branching (time division). Each of the branched laser beams obtained as above is condensed and injected onto an end face of a transmitting optical fiber by an injecting optical system, propagates in the transmitting optical fiber, exits from another end face of the fiber in an irradiating unit disposed in a remote processing site, and is condensed and applied to a processing point on a work to be processed by an irradiation optical system of the irradiating unit. For example, in the laser welding, a processing point of a two-layer metal plate is melted by the energy of a YAG laser beam and the melted portion solidifies and makes a weld nugget after the application of the laser beam.
However, for the above conventional laser beam processing apparatus, because the beam quality of the YAG laser light oscillation-outputted from a YAG laser is not so excellent, the precision and the efficiency of the multi-branching and the fiber transmission are poor and, as a result, the quality of the multi-point simultaneous processing and multi-position processing needs to be improved. That is, the beam divergence angle of a YAG laser light is so large that is not negligible in a multi-branching optical system and a fiber transmission optical system and, in addition, not only the beam divergence angle but also the beam mode (especially the lateral mode) are varied due to the thermal lens effect of the YAG rod. Therefore, problems have arisen that light convergence is poor, that accurate control of the power dividing ratio of the branched laser beams is difficult, etc. As a result, the problems influence the workability.